The broad objectives of this proposal are to examine the hypothesis of that human herpesviruses enhance the pathogenesis of periodontal disease. This hypothesis is based on the following observations. First, specific herpesviruses display tissue tropism in white blood cells during latency that allows them to enter areas of inflammation and contribute to the tissue destruction that occurs during periodontitis. Second, human herpesviruses are opportunistic pathogens that periodically reactivate. The intermittent pattern of reactivation and tissue breakdown is concordant with the relapsing-remitting course of periodontitis. Third, human herpesviruses can alter cytokine and chemokine production and dysregulate immune responses, leading to overgrowth of pathogenic bacteria. Based on these observations, this proposal focuses on the detection of human herpesvirus DNA and mRNA in periodontitis sites and tissue, as well as the biological interactions of herpesviruses with putative bacterial pathogens and cytokines. In Aim 1 we will determine the ability of human herpesviruses to enhance the pathogenesis of periodontal disease. This will be tested using three approaches: (i) a cross-sectional human study to determine the relationship of periodontal disease severity and the presence of HHVs at individual disease sites. Molecular procedures will be used to identify and quantify the prevalence of all eight HHVs in the oral cavity of this patient population. (ii) since HHVs remain latent in leukocytes that are attracted to periodontitis sites by inflammation, we will correlate the prevalence of HHVs within WBCs with periodontal inflammation and using a prospective, longitudinal study, we will also determine whether HHVs can be eliminated from diseased sites following mechanical therapy; and (iii) the in vivo significance of cytomegalovirus infection will be assessed using the rat model of periodontitis, including studies of antiviral agents and immunesuppression to alter the disease process. In Aim 2 we will characterize the bacterial and host defense mechanisms regulated by herpesvirus infection. These studies will be performed by: (i) analyzing attachment and invasion of P. gingivalis into CMV infected cells using gingival fibroblasts and oral epithelial cells as a models of viral lytic and latent infection, (ii) determining whether latently infected epithelial cells support CMV reactivation following challenge with putative periodontal pathogens, endotoxin, bacterial metabolites and byproducts, and (iii) elucidating the effects of viral and cellular IL-10 on the phagocytosis activities of macrophages. One of the greatest challenges in periodontology concerns the events that induce conversion from gingivitis to periodontitis or from stable to disease-active periodontitis. The proposed studies will clarify the pathogenic significance of herpesvirus infections in the development of periodontitis through comprehensive research involving human, animal and in vitro studies. As a result, novel approaches to the treatment of periodontitis and refractory periodontitis may be developed.